A multi-target observation system and its design method

Abstract

The present invention provides a multi-target observation system and a design method thereof, the system comprising: 3 continuously controllable coded seismic sources formed by sequentially delayed excitation; the continuously controllable coded seismic sources are combined with 6 streamers to form the observation system; each of the continuously controllable coded seismic sources is composed of a controllable coded seismic source array composed of 4 identical subarrays; the excitation mode of the 4 identical subarrays is excitation according to a certain time delay; the array composition of the seismic source in the conventional observation system is the same as the array of the continuously controllable coded seismic source, except that each subarray and each seismic source are excited simultaneously. The observation system of the present invention has the advantages of low cost, high feasibility, high density and high coverage times.

Description

Technical Field

[0001] The present invention relates to the field of marine geological survey and oil and gas exploration technology, and in particular to a multi-target observation system and a design method thereof. Background Art

[0002] In marine geological surveys and oil and gas resource exploration, the observation system is a key part of the seismic information acquisition system. Especially as the development of marine oil and gas moves towards the middle and deep layers, the geological and seismic conditions in the region are complex, and the design of a high-resolution and high-signal-to-noise ratio three-dimensional observation system is more important. In order to overcome complex geological conditions such as shadow areas and buried hills in caustic areas, widen the azimuth, and increase the number of coverage and density, conventional observation systems such as single-source unidirectional, single-source bidirectional, multi-source multi-unidirectional, and multi-source bidirectional observation systems have developed in the direction of "two wides and one high" such as long arrangement, wide azimuth, multi-azimuth, and rich azimuth, and have made certain progress. However, compared with conventional observation systems, the economic cost is too high, and the requirements for technology and equipment conditions are extremely high, making it difficult to carry out work in actual engineering applications. Therefore, the design of an observation system with universality, flexibility, low cost, high density, and high coverage is an urgent problem to be solved in the field of geophysics. Summary of the invention

[0003] The purpose of the present invention is to solve the defects of the above-mentioned prior art and to provide a multi-target ocean continuous controllable coding high-density and high-coverage observation system and its design method.

[0004] A multi-target observation system, comprising three continuously controllable coded seismic sources formed by sequentially delayed excitation; the continuously controllable coded seismic sources are combined with six streamers to form the observation system;

[0005] Each of the continuous controllable coded seismic sources is composed of a controllable coded seismic source array consisting of 4 identical sub-arrays;

[0006] The excitation mode of the four identical sub-arrays is to excite with a certain time delay.

[0007] Furthermore, in the above-mentioned multi-target observation system, the three continuously controllable coded sources are excited in the following manner: the second source is excited with a delay of 75ms, and the third source is excited with a delay of 75ms after the excitation of the second source is completed.

[0008] Furthermore, in the multi-target observation system as described above, the four identical subarrays are: subarray 1, subarray 2, subarray 3, and subarray 4; the excitation mode of the four subarrays is: subarray 1 is excited without delay, subarray 2 and subarray 3 are excited with a delay of 24ms, and subarray 4 is excited with a delay of 48ms.

[0009] Furthermore, in the multi-target observation system as described above, the sub-array spacing of the four identical sub-arrays is 25m, the total array capacity is 10560cu.in, and it is composed of 12 380cu.in, 16 250cu.in, 8 150cu.in, and 8 100cu.in air guns. The air gun working pressure is 2000psi, the sea water depth is set to 20m, the sea surface reflection coefficient is -0.9, the array is a planar array, and the array immersion depth is 9m.

[0010] Further, in the above-mentioned multi-target observation system, each of the sub-arrays is composed of 3 380cu.in, 4 250cu.in, 2 150cu.in, and 2 100cu.in air guns;

[0011] Wherein, two of the 380cu.in air guns are connected in parallel to form a first gun cluster; two of the 150cu.in air guns are connected in parallel to form a second gun cluster; two of the 250cu.in air guns are connected in parallel to form a third gun cluster;

[0012] The sub-array is formed by connecting one of the 380cu.in air guns, the first gun cluster, one of the 250cu.in air guns, the second gun cluster, two 100cu.in air guns connected in series, one of the 250cu.in air guns, and the third gun cluster in series;

[0013] The intervals between the first, second and third gun clusters and the air guns connected in series are all 2.57m; the interval between the two air guns forming the gun cluster is 0.8m;

[0014] The intervals between the two 100cu.in air guns and one 250cu.in air gun connected in series are both 2.5m.

[0015] Furthermore, the multi-target observation system as described above is composed of the continuously controllable coded source and 6 streamers, the streamer length is 6000m, the streamer spacing is 100m, the streamer laying depth is 8m, the track spacing is 12.5m, and the shot line spacing is 18.75m.

[0016] A design method for a multi-target observation system includes the following steps:

[0017] Step A, designing a controllable coded source array containing four identical sub-arrays, and simulating its sub-waves and spectra through a van der Waals non-ideal gas airgun wavelet model;

[0018] Step B, constructing a continuous controllable coded seismic source, wherein the continuous controllable coded seismic source is constructed by successively exciting three controllable coded seismic source arrays, and simulating its sub-wave and spectrum through a van der Waals non-ideal gas airgun wavelet model;

[0019] Step C, combining the continuously controllable coded source with six streamers to form an observation system;

[0020] Step D: Based on the observation system, when a single source is excited, it faces shallow targets, and when three sources are excited in sequence, they face medium-deep targets;

[0021] The excitation mode of the three controllable coded source arrays is: first excite source A, then excite source B after sailing 25m, and then excite sources ABC in sequence after sailing 25m again, and the interval excitation time of the three sources is 75ms.

[0022] Furthermore, in the design method of the multi-target observation system as described above, the sub-array spacing of the four identical sub-arrays is 25m, the total array capacity is 10560cu.in, and it is composed of 12 380cu.in, 16 250cu.in, 8 150cu.in, and 8 100cu.in air guns. The air gun working pressure is 2000psi, the sea water depth is set to 20m, the sea surface reflection coefficient is -0.9, the array is a planar array, and the array immersion depth is 9m.

[0023] Furthermore, according to the design method of the multi-target observation system as described above, the observation system consists of the continuously controllable coded source and 6 streamers, the streamer length is 6000m, the streamer spacing is 100m, the streamer laying depth is 8m, the track spacing is 12.5m, and the shot line spacing is 18.75m.

[0024] Further, in the design method of the multi-target observation system as described above, each of the subarrays is composed of 3 380cu.in, 4 250cu.in, 2 150cu.in, and 2 100cu.in air guns;

[0025] Wherein, two of the 380cu.in air guns are connected in parallel to form a first gun cluster; two of the 150cu.in air guns are connected in parallel to form a second gun cluster; two of the 250cu.in air guns are connected in parallel to form a third gun cluster;

[0026] The sub-array is formed by connecting one of the 380cu.in air guns, the first gun cluster, one of the 250cu.in air guns, the second gun cluster, two 100cu.in air guns connected in series, one of the 250cu.in air guns, and the third gun cluster in series;

[0027] The intervals between the first, second and third gun clusters and the air guns connected in series are all 2.57m; the interval between the two air guns forming the gun cluster is 0.8m;

[0028] The intervals between the two 100cu.in air guns and one 250cu.in air gun connected in series are both 2.5m.

[0029] Beneficial effects:

[0030] The present invention is based on the basic theory that the greater the absolute width of the seismic wavelet, the higher the resolution and the design concept of land controllable seismic sources. It utilizes the relationship between the excitation time and the wavelet signal receiving time, and regularly adjusts the excitation time of each subarray in the air gun array so that the pulse peak of each subarray in the subwave excited by the array is offset in time. Finally, a wide pulse wavelet controllable coded seismic source with a wavelength of 72ms is constructed, and then three controllable coded seismic sources are excited in succession to generate a continuously controllable coded seismic source, which is combined with a conventional observation system to finally form a low-cost, highly feasible, multi-target, continuously controllable, coded, high-density, and high-coverage observation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a design idea diagram of the multi-target continuously controllable coded high-density and high-coverage observation system described in the present invention;

[0032] Figure 2 This is a plan view of the controllable coded source array of the present invention;

[0033] Figure 3 The excitation sub-wave and spectrum diagram of the controllable coded source array described in the present invention;

[0034] Figure 4 This is a plan view of the large-capacity continuously controllable coded source array of the present invention;

[0035] Figure 5 The excitation sub-wave and spectrum diagram of the large-capacity continuously controllable coded source array described in the present invention;

[0036] Figure 6 Different frequency bands and dominant frequency diagrams of the excited sub-waves of the large-capacity continuously controllable coded source array described in the present invention;

[0037] Figure 7 It is a plan view of the observation system with continuous controllable coding, high density and high coverage times according to the present invention;

[0038] Figure 8 This is a plan view of the multi-target continuously controllable coded high-density and high-coverage observation system described in the present invention. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention is described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] The present invention provides a multi-target continuously controllable coded high-density and high-coverage observation system, which includes three continuously controllable coded seismic sources formed by sequentially delayed excitation; the continuously controllable coded seismic sources are combined with a conventional observation system to form the observation system;

[0041] Each of the continuous controllable coded seismic sources is composed of a controllable coded seismic source array consisting of 4 identical sub-arrays;

[0042] The excitation mode of the four identical sub-arrays is to excite with a certain time delay;

[0043] The array composition of the seismic sources in the conventional observation system is the same as the array of the continuously controllable coded seismic sources, except that each sub-array and each seismic source are excited simultaneously.

[0044] Furthermore, the three continuously controllable coded seismic sources are excited in the following manner: the second seismic source is excited with a delay of 75ms, and the third seismic source is excited with a delay of 75ms after the excitation of the second seismic source is completed.

[0045] In the embodiment of the present invention, 75ms is the wavelength of the sub-wave excited by a single earthquake source. The sequential delay of 75ms (150ms) is to completely separate the waveforms of the sub-waves excited by each earthquake source and to construct an ultra-wide pulse sub-wave with a wider waveform envelope.

[0046] Furthermore, the four identical subarrays are: subarray 1, subarray 2, subarray 3, and subarray 4; the excitation mode of the four subarrays is: subarray 1 is excited without delay, subarray 2 and subarray 3 are excited with a delay of 24ms, and subarray 4 is excited with a delay of 48ms. The subarray spacing of the four identical subarrays is 25m, the total array capacity is 10560cu.in, and it is composed of 12 380cu.in, 16 250cu.in, 8 150cu.in, and 8 100cu.in air guns. The working pressure of the air gun is 2000psi, the seawater depth is set to 20m, the sea surface reflection coefficient is -0.9, the array is a plane array, and the array is placed at a depth of 9m.

[0047] The advantage of this subarray is that it is mainly composed of large-capacity airguns, so the bubble effect can be better suppressed; the subarray spacing of 25m is to increase the subarray spacing so that the excitation of each subarray can be seen as a separate "seismic source". The main effect of this is to subdivide the surface element, and the surface element size is reduced from 12.5*25m to 6.25*6.25m; the airgun working pressure, water depth and sea surface reflection coefficient are all conventional parameters; the delayed excitation time of each subarray is to construct a wide pulse sub-wave.

[0048] Further, each of the sub-arrays is composed of 3 380cu.in, 4 250cu.in, 2 150cu.in, and 2 100cu.in air guns;

[0049] Wherein, two of the 380cu.in air guns are connected in parallel to form a first gun cluster; two of the 150cu.in air guns are connected in parallel to form a second gun cluster; two of the 250cu.in air guns are connected in parallel to form a third gun cluster;

[0050] The sub-array is formed by connecting one of the 380cu.in air guns, the first gun cluster, one of the 250cu.in air guns, the second gun cluster, two 100cu.in air guns connected in series, one of the 250cu.in air guns, and the third gun cluster in series;

[0051] The intervals between the first, second and third gun clusters and the air guns connected in series are all 2.57m; the interval between the two air guns forming the gun cluster is 0.8m;

[0052] The intervals between the two 100cu.in air guns and one 250cu.in air gun connected in series are both 2.5m.

[0053] Furthermore, the observation system consists of the continuously controllable coded source and 6 streamers, the streamer length is 6000m, the streamer spacing is 100m, the streamer laying depth is 8m, the track spacing is 12.5m, and the shot line spacing is 18.75m.

[0054] The present invention also provides a design method for a multi-target ocean continuous controllable coding high-density and high-coverage observation system, the design of which is as follows: Figure 1As shown, specifically, by reasonably regulating the excitation time of each sub-array in the airgun source array, the receiving time of the sub-wave signal excited by each sub-array is delayed, thereby causing the peak time of the main pulse of the sub-wave excited by each sub-array in the array to shift, and constructing the controllable coded source with a waveform envelope wider than that of the conventional array. On this basis, three of the controllable coded sources are continuously excited, that is, the same three controllable coded sources are delayed in sequence to form a large-capacity continuous controllable coded source. The large-capacity continuous controllable coded source is combined with a conventional observation system and a continuous controllable coded high-density and high-coverage observation system for multiple targets is constructed by adjusting the number of source excitations.

[0055] Specifically, the design method includes the following steps:

[0056] Step A, designing a controllable coded source array including 4 identical sub-arrays, and simulating its sub-waves and spectra through a van der Waals non-ideal gas airgun wavelet model;

[0057] The controllable coded source array is as follows: Figure 2 As shown, it is composed of 4 identical sub-arrays with a sub-array spacing of 25m. The total array capacity is 10560cu.in. It is composed of 12 380cu.in, 16 250cu.in, 8 150cu.in, and 8 100cu.in air guns. The air gun working pressure is 2000psi. The seawater depth is set to 20m, the sea surface reflection coefficient is -0.9, and the array is a planar array with an array immersion depth of 9m. The excitation mode of each sub-array is that sub-array 1 is excited without delay, sub-arrays 2 and 3 are excited with a delay of 24ms, and sub-array 4 is excited with a delay of 48ms. The excitation sub-waves and spectrum of the controllable coded source array are shown in FIG. Figure 3 shown.

[0058] Step B, using the three controllable coded seismic source arrays described in step A, successively exciting three controllable coded seismic source arrays to construct a large-capacity continuous controllable coded seismic source, and simulating its sub-wave and spectrum through the van der Waals non-ideal gas airgun wavelet model;

[0059] The large-capacity continuously controllable coded source is as follows Figure 4 As shown, it is composed of the controllable coded source arrays described in step A. The excitation mode of each single subarray in the controllable coded source array is: subarray 1 is excited without delay, subarrays 2 and 3 are excited with a delay of 24ms, and subarray 4 is excited with a delay of 48ms. The excitation mode between the three sources is that the second source is excited with a delay of 75ms, and the third source is excited with a delay of 75ms after the second source is excited. The excitation subwave and spectrum of the large-capacity continuous controllable coded source array are as follows: Figure 5 As shown, Figure 6 Shown are different frequency bands and dominant frequencies, among which Figure 6The different frequency bands and dominant frequencies shown in the figure are for different targets in the middle and deep layers. The frequency bands of 15-60Hz (dominant frequency 40Hz) can meet the exploration of shallow targets, and the frequency bands of 5-20Hz (dominant frequency 10Hz) and 1-5Hz (dominant frequency 2Hz) can meet the exploration of medium and deep targets.

[0060] Step C: combining the continuously controllable coded source described in step B with a conventional observation system (ie, 6 streamers) to form a continuously controllable coded high-density and high-coverage observation system.

[0061] The continuously controllable coded high-density and high-coverage observation system is as follows: Figure 7 As shown, the observation system consists of the large-capacity continuously controllable coded source in step B and 6 streamers, with a streamer length of 6000m, a streamer spacing of 100m, a streamer laying depth of 8m, a track spacing of 12.5m, and a shot line spacing of 18.75m.

[0062] Step D, based on the continuous controllable coded high-density and high-coverage observation system described in step C, for different targets in shallow, medium and deep layers, a single controllable coded source in step B and the three controllable coded sources in step B are stimulated respectively, so as to realize a continuous controllable coded high-density and high-coverage observation system for multiple targets.

[0063] The multi-target continuous controllable coding high-density and high-coverage observation system is as follows: Figure 8 shown. Figure 8 ABC represents that the controllable coded source in step A is excited every 25m of sailing. Specifically, the A source is excited first, and then the B source is excited after sailing 25m. After sailing 25m again, the three sources ABC are excited in sequence, and the interval between the three sources is 75ms. When a single source is excited, it faces a shallow target, and when the three sources are excited in sequence, they face a medium-deep target. The specific excitation method is as described in step (A) and step (B).

[0064] Example:

[0065] This example is based on the following basic assumptions: the length and width of the exploration area are 14km and 5km respectively, the deepest target layer depth is 4000m, and the acquisition method is bidirectional acquisition. Therefore, the specific steps of the source and observation system design are:

[0066] S01, controllable coded source array such as Figure 2As shown, it is composed of 4 identical sub-arrays, with a sub-array spacing of 25m, a total array capacity of 10560cu.in, and is composed of 12 380cu.in, 16 250cu.in, 8 150cu.in, and 8 100cu.in air guns. The air gun working pressure is 2000psi, the sea depth is set to 20m, the sea surface reflection coefficient is -0.9, the array is a plane array, and the array is placed at a depth of 9m. The excitation mode of each sub-array is that sub-array 1 is excited without delay, sub-arrays 2 and 3 are excited with a delay of 24ms, and sub-array 4 is excited with a delay of 48ms.

[0067] S02, large-capacity continuously controllable coded source array such as Figure 4 As shown, it is composed of three controllable coded seismic sources as described in step A. The excitation method of the single subarray inside each seismic source is as described in step (1) above. The excitation method between the three seismic sources is that the second seismic source is excited with a delay of 75ms, and the third seismic source is excited with a delay of 75ms based on the completion of the excitation of the second seismic source.

[0068] S03, continuous controllable coding high-density and high-coverage observation system such as Figure 7 As shown, the observation system consists of the large-capacity continuously controllable coded source in step B and 6 streamers, with a streamer length of 6000m, a streamer spacing of 100m, a streamer laying depth of 8m, a track spacing of 12.5m, and a shot line spacing of 18.75m.

[0069] S04, continuous controllable coded high-density and high-coverage observation system for multiple targets Figure 8 shown. Figure 8 ABC represents the controllable coded seismic source in step A that is excited every 25m of navigation. Specifically, when seismic sources A and B are excited separately, they face shallow targets, and when seismic sources A, B, and C are all excited, they face medium-deep targets. When a single seismic source is excited and three seismic sources are excited successively, the specific excitation method is as described in step S01 and step S02.

[0070] The specific parameters of the observation system obtained by the embodiment of the present invention are shown in Table 1, where the array composition of the seismic source in the conventional observation system is the same as the seismic source array proposed in the embodiment of the present invention, but each subarray and each seismic source are excited simultaneously. The continuous controllable coded high-density and high-coverage observation system for multiple targets proposed by the present invention has the advantages of smaller bins, 7 times higher coverage and coverage density than the conventional observation system.

[0071] Table 1 Parameter comparison between conventional observation system and the observation system of the present invention

[0072]

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multi-target observation system, characterized in that: It includes three sequentially delayed excitations of continuously controllable coded seismic sources and six streamers; when a single seismic source is excited, it faces shallow targets, and when three seismic sources are excited in sequence, they face medium-deep targets; the excitation method of the three controllable coded seismic source arrays is: firstly excite the A seismic source, then excite the B seismic source after sailing 25m, and then excite the ABC seismic sources in sequence after sailing 25m again, and the interval excitation time of the three seismic sources is 75ms; Each continuously controllable coded source is composed of a controllable coded source array consisting of 4 identical sub-arrays; The excitation mode of the four identical sub-arrays is to excite with a certain time delay; The three continuously controllable coded seismic sources are excited in the following manner: the second seismic source is excited with a delay of 75ms, and the third seismic source is excited with a delay of 75ms after the excitation of the second seismic source is completed; The four identical subarrays are: subarray 1, subarray 2, subarray 3, and subarray 4; the excitation modes of the four subarrays are: subarray 1 is excited without delay, subarray 2 and subarray 3 are excited with a delay of 24ms, and subarray 4 is excited with a delay of 48ms; The sub-array spacing of the four identical sub-arrays is 25m, the total array capacity is 10560cu.in, and it is composed of 12 380cu.in, 16 250cu.in, 8 150cu.in, and 8 100cu.in air guns. The working pressure of the air guns is 2000psi, the seawater depth is set to 20m, the sea surface reflection coefficient is -0.9, the array is a planar array, and the array sinking depth is 9m; The length of the towline is 6000m, the towline spacing is 100m, the towline sinking depth is 8m, the track spacing is 12.5m, and the shot line spacing is 18.75m; Each of the sub-arrays is composed of three 380cu.in, four 250cu.in, two 150cu.in, and two 100cu.in air guns; Among them, two of the 380cu.in air guns are connected in parallel to form a first gun cluster; two of the 150cu.in air guns are connected in parallel to form a second gun cluster; two of the 250cu.in air guns are connected in parallel to form a third gun cluster; The sub-array is formed by connecting one of the 380cu.in air guns, the first gun cluster, one of the 250cu.in air guns, the second gun cluster, two 100cu.in air guns connected in series, one of the 250cu.in air guns, and the third gun cluster in series; The intervals between the first, second and third gun clusters and the air guns connected in series are all 2.57m; the interval between the two air guns forming the gun cluster is 0.8m; The intervals between the two 100cu.in air guns and one 250cu.in air gun connected in series are both 2.5m.

2. A design method for a multi-target observation system according to claim 1, characterized in that: The following steps are involved: Step A, designing a controllable coded source array containing four identical sub-arrays, and simulating its sub-waves and spectra through a van der Waals non-ideal gas airgun wavelet model; Step B, constructing a continuous controllable coded seismic source, wherein the continuous controllable coded seismic source is constructed by successively exciting three controllable coded seismic source arrays, and simulating its sub-wave and spectrum through a van der Waals non-ideal gas airgun wavelet model; Step C, combining the continuously controllable coded source with six streamers to form an observation system; Step D: Based on the observation system, when a single source is excited, it faces shallow targets, and when three sources are excited in sequence, they face medium-deep targets; The three controllable coded source arrays are excited in the following manner: first, the A source is excited, and then the B source is excited after sailing for 25 meters. After sailing for another 25 meters, the ABC sources are excited in sequence, and the interval between the three sources is 75ms. The sub-array spacing of the four identical sub-arrays is 25m, the total array capacity is 10560cu.in, and it is composed of 12 380cu.in, 16 250cu.in, 8 150cu.in, and 8 100cu.in air guns. The working pressure of the air guns is 2000psi, the seawater depth is set to 20m, the sea surface reflection coefficient is -0.9, the array is a planar array, and the array sinking depth is 9m; The length of the towline is 6000m, the towline spacing is 100m, the towline sinking depth is 8m, the track spacing is 12.5m, and the shot line spacing is 18.75m; Each of the sub-arrays is composed of three 380cu.in, four 250cu.in, two 150cu.in, and two 100cu.in air guns; Among them, two of the 380cu.in air guns are connected in parallel to form a first gun cluster; two of the 150cu.in air guns are connected in parallel to form a second gun cluster; two of the 250cu.in air guns are connected in parallel to form a third gun cluster; The sub-array is formed by connecting one of the 380cu.in air guns, the first gun cluster, one of the 250cu.in air guns, the second gun cluster, two 100cu.in air guns connected in series, one of the 250cu.in air guns, and the third gun cluster in series; The intervals between the first, second and third gun clusters and the air guns connected in series are all 2.57m; the interval between the two air guns forming the gun cluster is 0.8m; The intervals between the two 100cu.in air guns and one 250cu.in air gun connected in series are both 2.5m.

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